1. Field of the Invention
An object of the invention is a device for the connection of an apparatus or appliance to a transmission channel that can be used in the field of home automation. The object of this field, which has a very promising future, is the interconnection, within a dwelling, of the various items of apparatus and appliances that use electricity so that their use can be managed as efficiently as possibly. These items of apparatus and appliances include central heating installations (for example those using electricity or hot water) and installations for the reception of radio broadcasts and communications installations as well as various domestic electrical appliances, notably freezers and washing machines. They may also include surveillance installations and fire or burglary alarms.
Experts studying these questions of home automation links have together and set up a standard governing the conditions under which signals, data elements or commands have to be transmitted. To this end, they have defined the following five transmission channels: transmission by carrier current, transmission by infrared radiation, radioelectric transmission, transmission by twisted pairs and transmission by coaxial cable. For each transmission channel, the standard defines the link physically as well as temporally. This means that the recognition signals, when a communication is set up, must follow to particular protocols of transmission and reception. Furthermore, in each channel, there is provision for transmission speeds that may vary, the low speeds being usable especially when the transmission channel is not a high-quality channel, i.e. especially when it is noise-ridden.
The items of apparatus that are designed to be connected to installations such as these are provided, by virtue of their principle, with a microprocessor or microcircuit capable of making the apparatus carry out instructions that have been transmitted to it by the channel or conversely of sending the channel indications, intended for an alarm station, on the efficient operation of the apparatus. Among the possible uses, it is possible to conceive of a case, for example, where electrical heating installations may be installations with time-delayed starting. This would be done at the initiative of the electricity supplier (a electricity production utility firm) in order to limit the magnitude of the drawing of current. There are instances when electrical power stations would find it difficult to cope with substantial drawing of current, as for example during a television broadcast when all the inhabitants of a region or even of a country start consuming power. Since the time taken to start up a power station is about half an hour, it would be possible notably with such installations to spread out the drawing of current so that it corresponds to the power build-up time of the power station. Thus, a microprocessor such as this, managing a heating installation in a house, would start up the heating and consequently the consumption of electrical power only during a time-slot with a preferential tarif or following a predetermined command from an electrical mains system.
For a system such as this to be usable, the devices for the connection of the appliances and items of apparatus to the transmission channel should meet these standards.
2. Description of the Prior Art
This has led to the making, initially, of wired circuits enabling the microprocessor of the apparatus to be coupled to the transmission channel. In view of the diversity of the microprocessors that can be used, as well as the large number and diversity of transmission channels possible (five channels not counting the cases of speed matching as well as the type of coding of the data signals), the development of this industry is hampered by the fact that it is complicated to implement.
In an attempt to overcome this drawback, a first French patent application No. 92 05423 filed on 30 April 1992 by the present applicant has devised a connection circuit using the microprocessor of the apparatus in such a way that, in addition to the instructions imposed on the apparatus, the microprocessor is capable of bringing about the execution of the instructions for the configuration of the connection so as to match the channel. This approach has had the merit of eliminating the presence of wired circuits, the operation of which was excessively related to the conditions of use and the development of which entailed a laborious process. At the same time, this approach has had one drawback: it requires all apparatus designers to have knowledge of the connection standard so that, in the microprocessor of their apparatus, they provide for a set of instructions appropriate to the setting up of the connection between the apparatus and the channel. This is unfortunately difficult to implement, especially at the present time when this industry is in the process of being established and when this standard is little known. This standard is a complex one: its contents, brought together in one document, take up as much space as a good-sized dictionary.
Notably, the problem in the foregoing approach that was conceived of arises out of the fact that the use of the apparatus and the connection protocol are done by one and the same microprocessor. Consequently, this makes it necessary to store a programme of instructions pertaining to this protocol and to the use in the memory of this microprocessor. Now, the location of the instruction pertaining to this protocol in the use to which the client puts the system is not known a priori and this makes it necessary, therefore, either that the customer should know the standard or that the customer should get his mode of use programmed by the designer of the channel connection device, which is a very cumbersome process.
Furthermore, in managing both the protocol and the use, the microprocessor of the apparatus performs less well than if it were to manage only one of the two tasks.
The standard stipulates, for a carrier current link, a speed of 2400 bauds with 66 bytes per frame in nominal mode. In a link using twisted pairs, the transmission speed is equal to 9600 bauds at 1.5 Mbits with 256 bytes per frame. With an infrared link, there is provision for 1200 bauds or 2400 bauds and 6 to 256 bytes per frame respectively while in RF links the transmission speed is in the range of 1 megabit per second.
The fact that a microprocessor is capable of managing such a diversity of protocols, given that these microprocessors also have to operate the appliance connected to the channel, entails a cost of about fifty French francs per unit for the connection device, even for production in large quantities whereas a low-cost (three or four francs) microprocessor would suffice to make the apparatus work. This approach can therefore be envisaged only for large machines or large installations. It is not feasible, for example, for an installation for a wall socket for electrical current.
It is an object of the invention to overcome these drawbacks, i.e. to make the standard transparent to users while at the same time also reducing the cost of the connection point. According to the invention, this problem is resolved by the use of a wired circuit connected, first, to the channel and, second, to the microprocessor. The difference between this wired circuit and prior existing ones is that it is programmable. In a connection device such as this, the principle of the programming of this wired circuit consists in providing for two intermediate registers in the. A first register is designed for control signals and a second register is designed for data elements. Each of these registers comprises a part called a transmission part and a part called a reception part, although these parts may be physically one and the same.
During transmission, a part of each of these registers is written, i.e. its cells are programmed, by the microprocessor of the appliance. Then, these cells are read by a circuit connected to the transmission channel. Conversely, for reception, the cells of these intermediate registers are written by a circuit connected to the transmission channel and are then read by the microprocessor. Seen from the apparatus side, the management of these registers (reading or writing) is simple since it uses a common technique for the reading and writing of computer type registers. Seen from the transmission channel side, the wired nature of the system enables it to take charge of all the difficulties of matching related to the transmission or reception of the information elements between the channel and the device.
The particular feature of the intermediate register moreover is that it provides adaptability for the connection device: notably, it enables it to achieve self-configuration in transmission speed for example, or in encoding mode (with even parity or odd parity or in any other mode). Given the various situations in which the wired circuit of the invention may be placed, it is realized that, in reception mode, when a message has been received, the external microprocessor will be required only to read the contents of this message in the data register and, when this message has been read, to report on the fact that it has been read. In transmission mode, the microprocessor of the apparatus will be required only to provide the device with information on the addressee of the transmission as well as on the contents of the message to be transmitted. From this viewpoint, the constraints of the standard disappear totally for the designer of an apparatus. Consequently, the microprocessor to be implemented in this apparatus may be very simple and its cost may be very low, for example three or four francs. As a result of this procedure, the standard is completely transparent to the user. He complies with it without knowing that he is doing so.